Various types of rotary drill bits have been used to form wellbores or boreholes in downhole formations. Such wellbores are often formed using a rotary drill bit attached to the end of a generally hollow, tubular drill string extending from an associated well surface. Rotation of a rotary drill bit progressively cuts away adjacent portions of a downhole formation using cutting elements and cutting structures disposed on exterior portions of the rotary drill bit. Examples of rotary drill bits include fixed cutter drill bits or drag drill bits, impregnated diamond bits and matrix drill bits. Various types of drilling fluids are generally used with rotary drill bits to form wellbores or boreholes extending from a well surface through one or more downhole formations.
Conventional borehole drilling in a controlled direction requires multiple mechanisms to steer drilling direction. Bottom hole assemblies have been used consisting of the drill bit, stabilizers, drill collars, heavy weight pipe, and a positive displacement motor (mud motor) having a bent housing. The bottom hole assembly is connected to a drill string or drill pipe extending to the surface. The assembly steers by sliding (not rotating) the assembly with the bend in the bent housing in a specific direction to cause a change in the borehole direction. The assembly and drill string are rotated to drill straight.
Other conventional borehole drilling systems use rotary steerable arrangements that use deflection to point-the-bit. They may provide a bottom hole assembly that may have a flexible shaft in the middle of the tool with an internal cam to bias the tool to point-the-bit. In these systems, an outer housing of the tool does not rotate with the drill string, but rather it may engage the sidewall of the wellbore to point-the-bit.